Field of the Invention
The present invention relates to an intermediate coating composition, a multilayered coating film, and a method for forming the multilayered coating film.
Discussion of the Background
For example, in a high-speed operation of automobiles, collision of pebbles and the like onto painted faces of outer panels of the automobiles is inevitable. Due to the collision of the pebbles and the like, damaging phenomena such as cracking and flaking on the coating film of the vehicle outer panel (chipping, as generally referred to) may be caused. When such chipping is caused, water and the like would penetrate from this area, and thus rusting of the foundation material of the outer panel may be caused.
Particularly, in cold foreign countries such as North America, Canada and North Europe, a large amount of rock salts and sand are dispersed on the road surface in winter season for thawing snow; therefore, chipping resistance on coating films of outer panels of automobiles, in particular, is important, and coating films not accompanied by breakage, flaking and the like of the coating film even if pebbles collided have been desired, whereby the foundation materials of vehicle outer panels would be prevented from rusting.
In general, in paint application of outer panels of automobiles, an electrodeposition paint (undercoating paint), an intermediate coating paint and a top coating paint are sequentially applied on a steel plate which had been subjected to iron phosphate/zinc phosphate chemical conversion coating. In order to improve chipping resistance and in turn, a rust-preventive property, chipping-resistant primers to be applied between an electrodeposition coating layer and an intermediate coating layer, and the like have been developed (see, Japanese Unexamined Patent Application, Publication Nos. H6-41494, H6-93227, H6-322059, H6-346024, H7-228834, H9-241580 and 2002-180000). However, coating of these chipping-resistant primers may result in an increase in production cost, contrary to demands for the present, i.e., a reduction in cost.
On the other hand, a technique of imparting chipping resistance to the intermediate coating layer was also developed (see, Japanese Unexamined Patent Application, Publication Nos. H4-77580 and 2011-50916). However, these techniques also fail to attain sufficient chipping resistance under the current situation.
Therefore, in the paint application of outer panels of automobiles, more superior chipping resistance is desired for the intermediate coating layer. The same applies to external paint application of motor cycles, automobile accessories, fork-lift trucks, heavy equipment, and the like.